Forces can be balanced or unbalanced, where balanced forces produce no motion and unbalanced forces produce motion; Newton's Three Laws of Motion define how forces cause changes in motion, such as how an applied force results in a change in momentum proportional to that force and acting in the direction of the force, and how every action has an equal and opposite reaction. Forces are measured in Newtons and examples include forces from fingers opening a book, magnets attracting, and gravity holding up objects.

2. FORCE
A PUSH OR PULL
ON A BODY IS
CALLED FORCE.
FORCES ARE
USED IN OUR
EVERYDAY
ACTIONS LIKE
PUSHING,
PULLING, LIFTING,
STRECHING,
TWISTING AND
PRESSING.

3. EFFECTS OF FORCE
• A force cannot be seen. A force can be
judged only by the effects which it can
produce in various bodies (or objects)
around us.
1.A force can move a stationary body.
2.A force can stop a moving body.
3.A force can change the speed of a moving
body.
4.A force can change the direction of a
moving body.
5.A force can change the shape and size of a
body.

4. BALANCED AND
UNBALANCED FORCE
• THERE ARE TWO KINDS OF FORCE:
• 1. BALANCED FORCE.
• 2. UNBALANCED FORCE.

5. BALANCED
FORCES
If the resultant of all the forces
acting on a body is zero, the
forces are called balanced
forces.
If a number of balanced
forces act on a stationary body,
the body continuous to remain
in its stationary position.
If a number of balanced
forces act on a body in uniform
motion, the body continuous to
be in its state of uniform
motion.
Though balanced forces
cannot produce motion in a
stationary body but can change
the shape of the body.

6. UNBALANCED
FORCE
If the resultant of all the
forces acting on a body is
not zero, the forces are
called unbalanced forces.
When an unbalanced
force acts on a body, it
produces motion in the
body. Also, an unbalanced
can stop a moving body.
If there were no
unbalanced force of
friction or air resistance, a
moving body would go on
for ever.

7. NEWTON’S LAW OF
MOTION
• NEWTON HAS GIVEN
THREE LAWS OF TO DEFINE
THE MOTION OF BODIES.
THESE LAWS ARE KNOWN
AS NEWTON’S LAWS OF
MOTION.

8. NEWTON’S FIRST
LAW OF MOTION
A body at rest will remain in
rest, and a body in motion
will continue in motion in a
straight line with uniform
speed, unless it is compelled
by an external force to
change its state of rest or of
uniform motion.
INERTIA: Inertia is that
property of a body due to
which it resists a change in
its state of rest or of uniform
motion.

9. MOMENTUM
The momentum of a body is defined
as the product of its mass and
velocity.
NOTE: the force required to stop a
moving body is directly
proportional to its mass and
velocity.
Thus, momentum= mass x velocity
or, p= m x v
where p= momentum
m= mass of the body
and, v = speed of the body
SI UNIT= the SI unit of momentum
is kilogram meters per second
(kg.m/s)

10. NEWTON’S SECOND
LAW OF MOTION
The rate of change of
momentum of a body is
directly proportional to
applied force, and takes place
in the direction in which
force acts.
Force= change in
momentum/time taken
f= mv-mu/t
f= m(v-u)/t. But we know
that v-u/t =a
f= m x a
force = mass x acceleration
SI UNIT: its SI unit is ‘force’.

11. NEWTON’S THIRD
LAW OF MOTION
Whenever one body exerts a force
on another body, the second body
exerts equal and opposite force to
the first body. OR,
To every action there is equal and
opposite reaction.
1.EX: the rocket works on the
principal of action and reaction.
2.When a bullet is fired from the
gun, a force sending the bullet
forward is equal to the force
sending the gun backward. But
due to high mass of the gun, it
moves only a little distance
backward and gives jerk.

12. CONSERVATION OF
MOMENTUM
When two or more bodies
act upon one another, their
total momentum remains
constant provided no
external forces are acting.
Momentum is neither
created nor destroyed.
Total momentum before
collision = total
momentum after collision

13. How is Force Measured?
• Measured in Newtons (N)
• The more Newtons, the greater
the force
• One tool to measure the force of
gravity is the spring scale

14. Examples of Force
• Fingers open a book
• Push buttons on a keyboard
• Gravity holds up a chair
• 2 magnets coming together
• The force that results from combining forces
Visible Forces
Invisible Forces

15. How to Measure Net Force
SAME
DIRECTION =
ADD
TOGETHER
20N + 25N = 45N
This is the NET FORCE
UNBALANCED FORCE
because it produces MOTION
Person # 1
Pushing with 20N
Force
Person # 2
Pushing with 25N
Force

16. How to Measure Net Force
OPPOSITE
DIRECTIONS =
SUBTRACT
25N - 10N = 15N
This is the NET FORCE
UNBALANCED FORCE
because it produces MOTION
Team # 1
Pulling with 25N
Force
Team # 2
Pulling with 10N
Force

17. How to Measure Net Force
OPPOSITE
DIRECTIONS =
SUBTRACT
37N - 37N = 0N
This is the NET FORCE
Wrestler # 1
Pushing with 37N
Force
Wrestler # 2
Pushing with 37N
Force BALANCED FORCE because
there is NO MOTION